Production of zirconium hydride



Sept. 16, 1947. P. P. ALEXANDER 2,427,339 PRODUCTION OF ZIRCONIUM HYDRIDE Filed March 2e, 1945 #ramas/v NER TV 645 HEL/UM ATTORNEYS Patented Sept. 16, 1947 NETE@ STATES PRODUCTEON OF ZIRCONl-UM HYDRIDE Peter l. Alexander, Beverly, Mass., assigner to Metal Hydrides Incorporated, Beverly, Mass., a corporation of Massachusetts Application March 26, 1945, Serial No. 584,356

15 Claims.

This invention relates to the production of zirconium hydride and has for its object certain improvements in the method of producing zirconium hydride.

- While it is known that zirconium hydride may be produced by reacting metallic zirconium with hydrogen gas at an elevated temperature, the resulting product is generally impure because the metallic zirconium employed as a starting material is generally impure. On account of its high melting point, 1700 C., its great tendency to combine with oxygen, hydrogen, nitrogen, carbon monoxide and carbon dioxide and the readiness with which it forms alloys with the common metals, the production of metallic zirconium in a state of purity is very diicult, although it is found in nature in larger quantities than many of the so-called common metals. Zirconium occurs as a silicate in Zircon and hyacinth and as an oxide in zirkite. It is prepared in various ways. For example, the iiuorine-potassium compound of zirconium is treated with aluminum or sodium to form silver gray scales or an amorphous black powder. Another method is to treat purified zirconium oxide with sodium, calcium, magnesium, or aluminum in a steel bomb by a thermit reaction. The resulting reaction mass is then removed from the bottom and subjected to a separate and special purification treatment operation to remove excess reducing metal. These methods obviously leave a great deal to be desired.

As a result of my investigations, I have discovered that zirconium hydride may be produced readily and eiiiciently by an improved pyrometallurgical method. When operating in the special manner herein disclosed, a reducing agent may be employed Which reacts with the zirconium compound to effect a substantially complete reduction, leaving a metallic zirconium product of high purity which may be converted promptly into zirconium hydride of high purity.

In accordance with the invention, a charge of zirconium compound and excess alkaline earth metal hydride is gradually heated in a reduction zone to a temperature suiiiciently high gradually to dissociate the alkaline earth metal hydride into alkaline earth metal and hydrogen gas and to reduce the zirconium compound in the charge with the alkaline earth metal thus released to form metallic zirconium and a compound of the alkaline earth metal. The-reaction zone is evacuated while at a temperature suiiiciently high t dissociate the excess alkaline earth metal hydride to remove hydrogen gas therefrom and to distill and pass the excess alkaline earth metal thus released from the charge into a body of absorbing material. Hydrogen gas is then admittedv to the heated reaction zone in amount sufcient to convert the reduced zirconium to zirconium hy- (Cl. 7a3-264) dride. The resulting charge containing'the zirconium hydride and compound of the alkaline earth metal is cooled, after which the zirconium hydride is separately recovered by leaching the charge with a solvent for the compound of the alkaline earth metal.

Various zirconium compounds, such as zirconium dioxide, zirconium chloride, zirconium iodide, or other halogen compound of zirconium, etc., may be thus treated to convert the available zirconium into a form of high purity which may then be converted into zirconium hydride of high purity. In a presently preferred practice of the invention, zirconium dioxide pigment is employed as the source of zirconium.

Among the reducing agents particularly adapted for the practice of. the invention are the alkaline earth metal hydride, such as the hydrides of calcium, strontium and barium, of which calcium hydride is the cheapest and therefore the most practical. The reducing metal of the compound should be readily volatilizable or distillable, because it is used in excess of the amount required theoretically to eiect the desired reduction, and the excess which doesnot actually enter into the reaction is distilled out of the charge and passed into the body of absorbing material, thus removing it from and keeping it out of Contact with the reduced zirconium.

The reaction zone is preferably evacuated in the beginning to remove air and moisture, and then filled with an inert gas. The inert gas is advantageously a monatomic gas, such as argon or helium, or a mixture of such gases. A suficient amount ofthe gas is fed into the reduction zone to raise its pressure to a point at which upwardmovement of the vapors of reducing metalis inhibited, the object being to keep the reducing metal in contact with the zirconium compound long enough t0 elect the desired reaction, and to prevent the distilled. excess reducing metal from rising or passing completely through the body of absorbing material. The effect othe pressure exerted by the gas is to retard upward movement of the distilled reducing metal until that movement isin fact wanted, in a later step.

The absorbingl material is advantageously a suitable metal oxide, such as zirconium dioxide, titanium dioxide, chromium oxide, etc., with which the excess distilled reducing metal may react, at least inY part. While the body of ab sorb'ing material may be removedfrom the charge of zirconium dioxide and reducing metal, it is highly advantageous to place it as a layer on top of the charge. InY a presently preferred practice of the invention, a layer of zirconium dioxide pigment, similar to the zirconium dioxide pigment in the charge, of suitable-thickness, is placed on top of the charge.

The charge of zirconium dioxide pigment and excess alkaline earth metal, with the layer of absorbing material, is heated in a reduction zone that has been advantageously evacuated to remove objectionable air and moisture, the air being replaced with a suitable inert gas, such as helium or argon, preferably-under substantial positive pressure, as pointed out above. I have found that a pressure of l pounds is effective under the conditions at present employed in the practice of the invention.

As the charge gradually rises in temperature the alkaline earth metal hydride gradually dissociates into hydrogen gas and alkaline earth metal. The alkaline earth metal thus released promptly reacts with the zirconium dioxide pigment to form metallic zirconium and an oxide of the alkaline earth metal. This reaction gradually progresses until the reduction goes to completion. The hydrogen gas released by dissociation of the alkaline earth metal hydride contacts the reduced zirconium particles and keeps their surfaces clean, fo-r example, from surface oxide. The excess alkaline earth metal hydride tends to remain as such at this stage of the operation. The reaction zone is then evacuated, while at a temperature suiciently high to dissociate the excess alkaline earth metal hydride to remove hydrogen gas, as well as other gaseous reaction products, such as steam, and to distill and pass the excess alkaline earth metal thus released from the charge into the layer of absorbing material. If, for example, the absorbing material is also zirconium dioxide, some of it may be reduced by the distilled excess reducing metal. Depending upon the temperature of the layer of absorbing material, some of the distilled excess reducing metal may be condensed therein and some of it, of course, may react with the zirconium dioxide. In any event, it is desired so to conduct the heating operation that the distilled excess reducing metal is retained in the absorbing material to prevent its co-ndensation and collection in areas removed from the absorbing material. Hydrogen gas is then admitted to the heated reaction zone in amount sufcient to convert the reduced zirconium to zirconium hydride; the charge being cooled if necessary to the hydriding temperature of the reduced zirconium. The resulting charge containing the hydrided zirconium particles and oxide of the alkaline earth metal is cooled. The charge is then leached with a solvent for the alkaline earth metal oxide to recover the zirconium hydride.

A charge of iinely divided and intimately ad- 'mixed zirconium dioxide pigment and excess calcium hydride, for example, is placed in a reaction zone and a layer of zirconium dioxide pigment is placed on top of the charge. The reduction zone is evacuated, preferably at an elevated temperature, to remove air and moisture; after which the reaction zone is iilled with helium or argon, preferably under positive pressure. The charge is gradually heated until the calcium hydride dissociates into calcium and hydrogen gas, and the reducing reaction sets The reaction may be indicated as follows:

And the combined dissociation and reducing reactions inay be indicated conveniently as follows:

CIT

As a result, the calcium hydride is initially dissociated into calcium, the desired reducing metal, and hydrogen gas; the calcium reduces the zirconium dioxide to zirconium and forms calcium oxide; and the hydrogen gas released by dissociation of the calcium hydride reacts with surface oxide on the reducedrzirconium particles to form moisture which is promptly converted into steam.

The reaction zone is then evacuated, while at a temperature sufficiently high to dissociate the excess calcium hydride, to remove hydrogen gas as well as to distill and pass the excess calcium from the charge into the absorbing layer of zirconium dioxide in which some or all of it reduces some `of the zirconium dioxide and in which some of it may be condensed.v The layer of zirconium dioxide should be suiliciently thick to catch and Vretain substantially all of the excess calcium as it rises from the underlying charge.

Hydrogen gas is then passed into the heated reaction zone in amount sufficient to convert the reduced zirconium in the charge to zirconium hydride, the reaction for which may be indicated as follows:

(e) Zr--CaG-l-ZI-Ig-ZrI-Ii-i-Ca@ Since the reducing reaction, equation (2) above, in which the freshly released calcium reacts with the zirconium dioxide to form calcium oxide and zirconium, takes place at a temperature higher than that at which the hydriding reaction of Equation l can take place, the charge is cooled, if necessary, to the hydriding temperature.

Various procedures may then be employed to recover the zirconium hydride in the main part of the charge. Thus, the resultant charge and top layer are permitted to cool, after which they are removed from `the reaction zone.

There is a clear line of demarcation between the resultant charge and top layer. The charge tends to be a sintered mass of calcium oxide and zirconium hydride particles, whereas the absorbing layer of zirconium dioxide containing the excess distilled calcium tends to remain in a fluffy condition and may be readily shaken off or brushed away.

The resultan-t charge containing the calcium oxide and zirconium hydride may be treated, in any suitable manner to separate the two. The -calcium oxide may be removed by leaching the charge, preferably in crushed form, with a suitable solvent, for example dilute acid, such as hydrochloric, sulfuric, or acetic, or a solution of ammonium salt, in which it is soluble, but in which the zirconium hydride is substantially insoluble.

These and other features of the invention will be better understood by referring to the accompanying drawing, taken' in conjunction with the following description, which diagrammatically illustrates an apparatus adapted for a practice of the invention.

The apparatus shown comprisesan outer retort l supported withinV a heating furnace Il, the retort being held in position by means of a plurality of supports l2 spaced under and around a circumferential flange of the retort and resting on the top of the heating furnace. The retort Vis made preferably of heat-resistant steel. It is provided with a removable cover i3 having attached thereto a vertical pipe ifi with lateral valved branchesV l5 and i6 and Vertical valved branch l'i connectible with a source of vacuum,

inert gas, such as helium or argon, and, hydrogen gas, respectively, A gasket i8 is disposed between the cover and the flanged top portion of the outer retort, the three elements forming a non-leakable connection by means of a plurality of spaced bolts IS. A removable inner retort 20 having an open top rests within the outer retort The heating furnace consists essentially of a box-like chamber 2| having a refractory bottom 22, side and end walls 23 anda top 213 with an opening of a size adapted to receive the outer retort. An expanding opening 25 is provided at or near a lower corner of one of the side walls of the chamber, for the introduction of heating gases into the chamber. A flue opening 28 extends through another wall, preferably at a higher level, so that heating gases passed into the chamber through opening 25 tend to pass around and in contact with the outer retort before leaving the chamber through the flue opening.

The apparatus may be used as follows: A charge of finely divided and intimately admixed zirconium dioxide pigment and excess calcium hydride, for example, is placed in the bottom ci inner retort 2li. An absorbing layer of zirconium dioxide pigment is placed on the top ci the charge, the layer being of suitable thickness and spread uniformly across the entire top ci the charge. The inner retort is then placed in outer retort l, gasket i8 is placed in position on the flanged portion of the top of the outer retort, and removable cover i3 is securely bolted thereon to make a non-leaking joint.

With the valves in lateral branch I6 and vertical branch l1 closed, the valve in lateral branch l5 is opened and the retorts are placed under Vacuum to remove objectionable air and moisture. Heating gases are passed through opening 25 into furnace chamber 2l. The retorts are kept under vacuum preferably as the charge rises in temperature to facilitate removal of the air and moisture. Before the charge reaches a temperature at which the calcium hydride dissociates and reduction of the zirconium dioxide in the charge takes place, the valve in lateral branch I5 is closed and that in lateral branch I6 is opened to iill the retorts with inert gas, for example helium, preferably under pressure, for example pounds. The introduction of heating gases into chamber 2l is continued to raise the temperature of the charge to the point at which dissociation of the calcium hydride and reduction of the zirconium dioxide in the charge take place. When the reduction has gone to completion, with the valve in lateral branch It closed, the valve in lateral branch I5 is opened to evacuate the retorts. The temperature is sufliciently high to dissociate the excess calcium hydride in the charge as evacuation takes place. As a result, hydrogen previously released and hydrogen released at this stage, the inert gas and gaseous products of reaction are removed from the retorts. and passed from the charge into the absorbing layer of zirconium dioxide, where it reacts at least in part with some of the zirconium dioxide. If the temperature of the layer is suiciently low, some of the calcium may be condensed therein. In any event, the layer of zirconium dioxide should be sumciently deep to retain substantially all of the distilled excess calcium, either as such or as calcium oxide, so that calcium does not condense on the upper part of the inner or outer retort, on the cover or in the vertical pipe and lateral branches.

The excess calcium released is distilled i The valve in lateral branch l5 is closed; the valve in lateral branch IB is preferably opened to admit inert gas to the reaction zone, under substantial positive pressure; and the valve in vertical branch I'l is opened to admit enough hydrogen gas to convert the reduced zirconium in the charge to zirconium hydride. As indicated above, the temperature of the charge may be dropped to that at which the desired hydriding reaction can take place.

The retorts and hence the resulting charge and absorbing layer are permitted to cool. Cover i3 is removed; inner retort 20 is withdrawn from outer retort l0 and its contents are removed therefrom. A clear line of demarcation tends to exist between the resulting absorbing layer and the underlying charge. The absorbing layer of zirconium dioxide containing the distilled excess calcium remains essentially in a uify condition. The underlying charge containing the zirconium hydride and calcium oxide is a more or less sintered coherent mass. It is therefore a simple matter to separate the two. The uiy top layer may be brushed orf the underlying charge.

Since the top layer consists of zirconium dioxide, the reduction of some of it by the distilled excess calcium does not contaminate the initial reduced zirconium or the final zirconium hydride in the underlying charge. Under normal operating conditions, the temperature of the top or absorbing layer is sufficiently high to cause all or most of the distilled excess calcium to react with the zirconium dioxide to form calcium oxide and reduce some of the zirconium dioxide. If any of the distilled excess calcium should condense as such in the top or absorbing layer, it would react with the hydrogen gas admitted to hydride the reduced zirconium, to form calcium hydride; which would, of course, be admixed with the calcium oxide and zirconium dioxide in the top or absorbing layer. In any event, it does not contaminate the reduced zirconium then initially present in the underlying charge or the zirconium hydride finally present in the underlying charge. In other words, zirconium hydride of high purity may be formed conveniently in the practice of the invention. The zirconium hydride in the underlying charge is separately recovered in any suitable manner. For example, the charge is preferably crushed, after which the calcium oxide may be eliminated by leaching the charge with a suitable solvent, such as a dilute acid, for example hydrochloric, sulfuric, or acetic acid, or a solution of ammonium salt. The free zirconium hydride may then be suitably treated to place it in marketable form, such as bars or powder.

While in the example described, calcium hydride is the reducing metal compound employed, other reducing agents can be employed, such as the hydrides of other alkaline earth metals. The oxide of any of the alkaline earth metals, formed as a result of the reducing reaction, may be similarly eliminated from the resulting underlying charge by leaching.

It will be clear to those skilled in this art that the method of the invention lends itself to a number of useful modications and that the above-described practice is only by way of illustration.

I claim:

1. In the production `of zirconium hydride, the improvement which comprises gradual-1y heating a charge of zirconium compound and alkaline 'earth metal hydride in a reaction zone to a temperature sufficiently high gradually to dissociate the alkaline earth metal hydride into alkaline earth metal and hydrogen gas and to reduce the zirconium compound in the charge with the alkaline earth metal thus released to form metallic zirconium and a compound of the alkaline earth metal, the alkaline earth metal hydride being present in amount suicient to yield on dissociation the reducing alkaline earth metal in excess of the amount required to effect reduction of the zirconium compound, evacuating the reaction zone While at a temperature sufliciently high to dissociate the excess alkaline earth metal hydride to remove hydrogen gas and gaseous products of reaction therefrom and to distill and pass the excess alkaline earth metal thus released from the charge into a body of absorbing material, introducing hydrogen gas into the heated reaction zone in amount sucient to convert the reduced zirconium to zirconium hyride, cooling the resulting charge containing the zirconium hydride and compound of the alkaline earth metal, and separately recovering the zirconium hydride by leaching the `charge with a solvent for the compound of the alkaline earth metal.

v2. In the production of zirconium hydride, the improvement which comprises gradually heating a charge of zirconium compound and alkaline earth metal hydride in a reaction zone containing an inert gas in amount to place the reaction zone under substantial positive pressure to Ia temperature suiciently high gradually to dissociate the alkaline earth metal hydride into alkaline earth metal and hydrogen gas and to reduce the zirconium compound in the charge with the alkaline earth metal thus released to form metallic zirconium and a compound of the alkaline earth metal, the alkaline earth metal hydride being present in amount suflicient to yield on dissociation the reducing alkaline earth metal in excess of the amount required to effect reduction of the zirconium compound, evacuating the reaction zone While at a temperature suiiiciently high to dissociate the excess alkaline earth metal hydride to remove hydrogen gas, the inert gas and gaseous products of reaction therefrom and to ydistill and pass the excess aikaline earth metal thus released from the charge into a body of absorbing material, introducing hydrogen gas into the heated reaction zone in amount suicient to convert the reduced zirconium to zirconium hydride, cooling the resulting charge containing the zirconium hydride and compound of the alkaline earth metal, and separately recovering the zirconium hydride by leaching the charge With a solvent for the compound of the alkaline earth metal.

3. In the production of zirconium hydride, the improvement which comprises gradually heating a charge of zirconium dioxide pigment and alkaline earth metal hydride in a reaction zone to a temperature sufciently hightgradually to dissociate the alkaline earth metal hydride into alkaline earth metal and hydrogen gas and to reduce the zirconium dioxide in the charge with the alkaline earth metal thus released to form metallic zirconium and an oxide of the alkaline earth metal, the alkaline earth metal hydride being present in amount sufficient to yield on dissociation the reducing alkaline earth metal in excess of the amount required to eect reduction of the zirconium dioxide, evacuating the reaction ,zone While at a ltemperature suicientlyrhigh to dissociate 'the excess alkaline earth metal hy'- ride to remove hydrogen gas and gaseous products of reaction therefrom and to distill and pass the excess alkaline earth metal thus released from the charge into an absorbing body of zirconium dioxide pigment, introducing hydrogen gas into the heated reaction zone in amount suiiicient to convert the reduced zirconium to zirconium hydride, cooling the resulting charge containing the zirconium hydride and the oxide of the alkaline earth metal, and separately recovering the zirconium hydride by leaching the charge with a solvent for the oxide of the alkaline earth metal.

4. In the production of zirconium hydride, the improvement which comprises gradually heating a charge of zirconium dioxide pigment and alkaline earth metal hydride in a reaction zone to a temperature suiliciently high gradually to dissociate the alkaline earth metal hydride into alkaline earth metal and hydrogen gas and to reduce the zirconium dioxide in the charge with the alkaline earth metal thus released to form metallic zirconium and an oxide of the alkaline earth metal, the alkaline earth metal hydride being present in amount suicient to yield on dissociation the reducing alkaline earth metal in excess of the amount required to eiect reduction oi the zirconium dioxide, evacuating the reaction zone While at a temperature suiciently high to dissociate the excess alkaline earth metal hydride to remove hydrogen gas and gaseous products of reaction therefrom and to distill and pass the excess alkaline earth metal thus released from the charge into an absorbing body of titanium dioxide pigment, introducing hydrogen gas into the heated reaction zone in amount sufficient to convert the reduced zirconium to zirconium hydride, cooling the resulting charge containing the zirconium hydride and the oxide of the alkaline earth metal, and separately recovering the zirconium hydride by leaching the charge with a solvent for the oxide of the alkaline earth metal.

5. In the production of zirconium hydride, the improvement which comprises gradually heating a charge of zirconium dioxide pigment and alkaline earth metal hydride in a reaction zone to a temperature sumciently high gradually to dissociate the alkaline earth metal hydride into alkaline earth metal and hydrogen gas and to reduce the zirconium dioxide in the charge with the alkaline earth metal thus released to' form metallic zirconium and an oxide of the alkaline earth metal, the alkaline earth metal hydride being present in amount sulicient to yield on dissociation the reducing alkaline earth metal in excess of the amount required to effect reduction of the zirconium dioxide, evacuating the reaction zone While at a temperature sufficiently high to dissociate the excess alkaline earth metal hydride to remove hydrogen gas and gaseous products of reaction therefrom and to distill and pass the excess alkaline earth'metal thus released from the charge into an absorbing body of chromium oxide pigment, introducing hydrogen gas into the heated reaction zone in amount sulicient to convert the reduced zirconium to zirconium hydride, cooling the resulting charge containing the zirconium hydride and the oxide of the alkaline earth metal, and separately recovering the zir- Vconium hydride by leaching the charge with a solvent for the oxide of the alkaline earth metal.

6. In the production of zirconium hydride, the improvement which comprises placing a charge l w of zirconium dioxide pigment and :alkaline earth metal hydride in a reaction zone, placing a layer of absorbing material on top of the charge, gradually heating the charge to a temperature suiiciently high gradually to dissociate the alkaline earth metal hydride into alkaline earth metal and hydrogen gas to reduce the titanium dioxide in the charge with the alkaline earth metal thus released to form metallic zirconium and lan oxide of the alkaline earth metal, the alkaline earth metal hydride being present in amount suiiicient to yield on dissociation the reducing alkaline earth metal in excess of the amount required to eiect reduction of the zirconium dioxide, evacuating the reaction zone while at a temperature sulciently high to dissociate the excess alkaline earth metal hydride to remove hydrogen gas and gaseous products of reaction therefrom and to distill and pass the excess alkaline earth metal thus released from the underlying charge into the overlying layer of absorbing material, introducing hydrogen gas into the heated reaction zone in amount suiiicient to convert the reduced zirconium to zirconium hydride, cooling the resulting charge containing the zirconium hydride and the oxide of the alkaline earth metal, separating the overlying layer of absorbing material from the underlying charge, and separately recovering the zirconium hydride by leaching the charge with a solvent for the oxide of the alkaline earth metal.

7. In the production of zirconium hydride, the improvement which comprises placing a charge of zirconium dioxide pigment and alkaline earth metal hydride in a reaction zone, placing a layer of absorbing material on top of the charge, gradually heating the charge in the presence of an inert gas maintained under substantial positive pressure to a temperature suiciently high gradually to dissociate the alkaline earth metal hydride into alkaline earth metal and yhydrogen gas to reduce the zirconium dioxide in the charge with the alkaline earth metal thus released to form metallic zirconium and an oxide of the alkaline earth metal, the alkaline earth metal hydride being present in amount suicient to yield on dissociation the reducing alkaline earth metal in excess of the amount required to effect reduction of the zirconium dioxide, evacuating the reaction zone While at a temperature suiliciently high to dissociate the excess alkaline earth metal hydride to remove hydrogen gas, the inert gas and gaseous products of reaction therefrom and to distill and pass the excess alkaline earth metal thus released from the underlying i charge into the overlying layer of absorbing material, introducing hydrogen gas into the heated reaction zone in amount sulcient to convert the reduced zirconium to zirconium hydride, cooling the resulting charge containing the zirconium hydride and the oxide of the alkaline earth metal, separating the overlying layer of absorbing material from the underlying charge, and separately recovering the zirconium hydride by leaching the charge with a solvent for the oxide of the alkaline earth metal.

8. In the production of zirconium hydride, the improvement which comprises placing a charge of zirconium dioxide pigment and alkaline earth metal hydride in a reaction zone, placing an absorbing layer of zirconium dioxide pigment on top of the charge, gradually heating the charge to a temperature sufficiently high gradually to dissociate the alkaline earth metal hydride into alkaline earth metal and hydrogen gas to reduce l the zirconium dioxide in the charge With the alkaline earth metal thus released to form metallic zirconium and an oxide of the alkaline earth metal, the alkaline earth metal hydride being present in amount suicient to yield on dissociation the reducing alkaline earth metal in excess of the amount required to effect reduction of the zirconium dioxide, evacuating the reaction zone while lat a temperature sufciently high to dissociate the excess alkaline earth metal hydride to remove hydrogen gas and gaseous products of reaction therefrom and to distill and pass the excess alkaline earth metal thus released from the underlying charge into the overlying layer of zirconium dioxide pigment, introducing hydrogen gas into the heated reaction zone in amount sucient to convert the reduced zirconium to zir- Y,

conium hydride, cooling the resulting charge containing the zirconium hydride and the oxide of the alkaline earth metal, separating the overlying layer of absorbing material from the underlying charge, and separately recovering the zirconium hydride by leaching the charge With la solvent for the oxide of the alkaline earth metal.

9. ln the production of zirconium hydride, the improvement which comprises placing a charge of zirconium dioxide pigment and calcium hydride in a reaction zone, placing a layer of absorbing material on top of the charge, gradually heating the charge to a temperature sufficiently high gradually to dissociate the calcium hydride into calcium and hydrogen gas to reduce the zirconium dioxide in the charge with the calcium thus released to form metallic zirconium and calcium oxide, the calcium hydride being present in amount sulcient to yield on dissociation the reducing calcium metal in excess of the amount required to effect reduction of the titanium dioxide, evacuating the reaction zone While at a temperature sufficiently high to dissociate the excess calcium hydride to remove hydrogen gas and gaseous products of reaction therefrom and to distill and pass the excess calcium thus released from the underlying charge into the overlying layer of absorbing material, introducing hydrogen gas into the heated reaction zone in amount sufficient to convert the reduced zirconium to zirconium hydride, cooling the resulting charge containing the zirconium hydride and the calcium oxide, separating the overlying layer of absorbing material from the underlying charge, and separately recovering the zirconium hydride by leaching the charge with a solvent for the calcium oxide.

10. In the production of zirconium hydride, the improvement Which comprises placing a charge of zirconium dioxide pigment and calcium hydride in a reaction zone, placing an absorbing layer of metal oxide on top of the charge, gradually heating the charge to a temperature suiiciently high gradually to dissociate the calcium hydride into calcium and hydrogen gas to reduce the zirconium dioxide in the charge With the calcium thus released to form metallic zirconium and calcium oxide, the calcium hydride being present in amount sufcient to yield on dissociation the reducing calcium metal in excess of the amount required to effect reduction of the titanium dioxide, evacuating the reaction zone While at a temperature sufficiently high to dissociate the excess calcium hydride to remove hydrogen gas and gaseous products of reaction therefrom and to distill and pass the excess calcium thus released from the underlying charge into the overlying layer of metal oxide, introducing hydrogen gas into the heated reaction zone in amount suicient to convert the reduced zirconium to zirconium hydride, cooling the resulting charge containing the zirconium hydride and the calcium oxide, separating the overlying layer of absorbing material from the underlying charge, and separately recovering the zirconium hydride by'leaching the charge with a solvent for the calcium oxide.

11. In the production of zirconium hydride, the improvement which comprises placing a charge of zirconium dioxide pigment and calcium hydride in a reaction zone, placing an absorbing layer of zirconium dioxide pigment on top of the charge, gradually heating the charge to a temperature suiciently high gradually to dissociate the alkaline earth metal hydride into calcium and hydrogen gas to reduce the zirconium dioxide in the charge with the calcium thus released to form metallic zirconium and calcium oxide, the calcium hydride being present in amount sucient to yield on dissociation the reducing calcium metal in excess of the amount required to effect reduction of the titanium dioxide, evacuating the reaction zone While at a temperature suciently high to dissociate the excess calcium hydride to remove hydrogen gas and gaseous products of reaction therefrom and to distill and pass the excess calcium thus released from the underlying charge into the overlying layer of zirconium dioxide pigment, introducing hydrogen gas into the heated reaction zone in amount sufficient to convert the reduced zirconium to zirconium hydride, cooling the resulting charge containing the zirconium hydride and the calcium oxide, separating the overlying layer of absorbing material from the underlying charge, and separately recovering the zirconium hydride by leaching the charge With a solvent for the calcium oxide.

12. In the production of zirconium hydride, the improvement which comprises placing a charge of zirconium dioxide pigment and calcium hydride in a reaction zone, placing an absorbing layer of zirconium dioxide pigment on top of the charge, evacuating the reduction zone to remove air and moisture, gradually heating the charge to a temperature suciently high gradually to dissociate the alkaline earth metal hydride into calcium and hydrogen gas to reduce the zirconium dioxide in the charge with the calcium thus released to form metallic zirconium and calcium oxide, the calcium hydride being present in amount suicient to yield on dissociation the reducing calcium metal in excess of the amount required to eiect reduction of the titanium dioxide, evacuating the reaction zone While at a temperature suiiiciently high to dissociate the excess calcium hydride to remove hydrogen gas and gaseous products of reaction therefrom and to distill and pass the excess calcium thus released from the underlying charge into the overlying layer of zirconium dioxide pigment, introducing hydrogen gas into the heated reaction zone in amount sufficient to convert the reduced zirconium to zirconium hydride, cooling the resulting charge containing the zirconium hydride and the calcium oxide, separating the overlying layer of absorbing material from the underlying charge, and separately recovering the zirconium hydride by leaching the charge With a solvent for the calcium oxide.

13. In the production of zirconium hydride,

lil

the improvement Which comprises placing a charge of zirconium dioxide pigment and calcium hydride in a reaction zone, placing an absorbing layer of zirconium dioxide pigment on top of the charge, evacuating the reaction zone to remove air and moisture, lling the reaction zone with an inert gas, maintaining the reaction zone under substantial positive pressure with said inert gas, gradually heating the charge to a temperature suiiciently high gradually to dissociate the alkaline earth metal hydride into calcium and hydrogen gas to reduce the zirconium dioxide in the charge With the calcium thus released to form metallic zirconium and calcium oxide, the calcium hydride being present in amount sumcient to yield on dissociation the reducing calcium metal in excess of the amount required to effect reduction of the titanium dioxide, evacuating the reaction zone While at a temperature suciently high to dissociate the excess calcium hydride to remove hydrogen gas, the inert gas and gaseous products of reaction therefrom and to distill and pass the excess calcium thus released from the underlying charge into the overlying layer of zirconium dioxide pigment, introducing hydrogen gas into the heated reaction zone in amount sufcient to convert the reduced zirconium to zirconium hydride, cooling the resulting charge containing the zirconium hydride and the calcium oxide, separating the overlying layer of absorbing material from the underlying charge, and separately recovering the' zirconium hydride by leaching the charge with 1a solvent for the calcium oxide.

14. In a method wherein a charge comprising a zirconium compound and an alkaline earth metal hydride is heated to a temperature sufciently high to dissociate the alkaline earth metal hydride into alkaline earth metal and hydrogen gas and to reduce the zirconium compound With the alkaline earth metal thus released to form the metal of said compound and a compound of the alkaline earth metal, the alkaline earth metal hydride being present in amount sufficient to 2' yield on dissociation the reducing alkaline earth metal in excess of the amount required to effect reduction of said zirconium compound, the improvement which comprises externally heating the charge together with a separate overlying layer or an absorbing material sufficiently high to reduce said zirconium compound and to distill and pass the excess alkaline earth metal from the charge into the separate layer of absorbing material, said absorbing material being a metal oxide with Which the excess distilled alkaline earth metal is capable of reacting.

l5. In a method wherein a charge comprising a zirconium compound and a reducing metal is heated to a temperature suiciently high to reduce the zirconium compound and form a compound of the reducing metal, the reducing metal being present in amount in excess of that required to effect reduction of said zirconium compound, the improvement which comprises externally heating the charge together with a separate overlying layer of an absorbing material 

